The invention disclosed herein relates generally to lighting control apparatus and methods, and more particularly to lighting controls which provide nonabrupt changes in luminance to achieve eye comfort and speed eye adaptation to different illumination intensities.
It is well known that rapid changes in lighting intensity affect comfort and ability to see. For example, turning on a bright bathroom light during the night or going from a dark restaurant or bar into the bright outdoor sun causes considerable temporary eye discomfort. Ability to see is also temporarily impaired.
Similarly, when passing from a brightly lit area into a dark place, ability to see is impaired for a longer time. For example, when entering a dark movie theater, it may be difficult at first even to see which seats are empty. However, after a few minutes the surroundings can be seen quite well.
The foregoing phenomenon is described, explored and analyzed in detail in numerous references, of which the following are representative examples.
Baker, H. D., "Initial Stages of Dark and Light Adaptation", Journal of the optical society of America, 53(1), 1963, pp. 98-103.
Baker, H. D., "Some Direct Comparisons Between Light and Dark Adaptation", Journal of the Optical Society of America, 45(10), 1955, pp. 839-844.
Baker, H. D., "The Course of Foveal Light Adaptation Measured by the Threshold Intensity Increment", Journal of the Optical Society of America, 39(2), 1949, pp. 172-179.
Boyce, P. R., Human Factors in Lighting. New York: MacMillan, 1981.
Brown, K. T., "Physiology of the Retina", Medical Physiology, C.V. Mosby Co., 1974.
Hopkinson, R. G. and Collins, J. B., The Ergonomics of Lighting, MacDonald & Co., 1970.
Luckiesh, M., The Science of Seeing, Van Nostrand, 1973.
Records, R.E., Physiology of the Human Eye and visual System, Harper & Row, 1977, pp. 368-372.
As described in these references, the actual process of eye adaptation to changes in illumination intensity has three components. The first component is characterized by a rapid adjustment, and presumably involves neural mechanisms. A second component characterized by medium time adjustment involves change in pupil size. A third component characterized by relatively slow adjustment is governed by the rates of photochemical processes at the cones and rods of the retina.
The overal rate of adaptation is governed by the slow photochemical phase, the actual time taken depending on the starting and final luminances. This is because the adaptation processes for rods and cones have different time constants, on the order of two minutes for cones and seven to eight minutes for rods. In general, when both starting and final luminances are in the photopic range, adaptation is relatively rapid. The adaptation time is typically a few minutes because only the cones are involved.
When the starting luminance is in the photopic range and the final luminance is in the scotopic range, a much longer two stage process occurs. The first stage involves the cones and the second stage involves the rods. Complete adaptation to darkness from a high photopic luminance can take up to an hour.
When both starting and final luminances are in the scotopic range, then only the rods are involved and adaptation is fairly rapid, typically on the order of several minutes.
Thus, it is apparent that benefits can be in the areas of eye comfort and improved seeing can be achieved by avoiding rapid changes in illumination intensity.
A variety of lighting control techniques and systems which provide for dimming or fading are alos well known. These range from simple, manually controlled dimmers implemented with variable resistors and/or silicon controlled rectifier chopping circuits to elaborate, computer controlled, programmable systems for a light level control. It is also known to use photodiodes or other light sensors to measure ambient light level, and to adjust illumination brightness in accordance with the sensed ambient luminance.
However, none of the known systems appear to specifically take into account the adaptation characteristics of the human eye, or to have as a specific objective the tailoring of changes in illumination intensity to the ability of the human eye to respond. The benefits to be gained from controlling changes in illumination intensity to adaptation characteristics of the eye include reducing discomfort when moving from dark to bright areas, reducing impact of transitions from dark to light to dark on darkadapted eyes, and saving energy when increased lighting levels do not improve discrimination.
The applicants have specifically considered the adaptation characteristics of the human eye in devising a unique light control method and apparatus which are based on controlling changes in luminance so that the rate of change tracks adaptability of the human eye to changes in luminance, thus achieving the foregoing benefits. Accordingly, many of the shortcomings of prior variable intensity lighting control systems are avoided.